The present invention relates to minimally invasive and catheter delivered embolic capture devices for use in the vasculature, especially those suited for usage in the brain and vessel systems perfusing the same.
Several acute stroke therapy trials were reported in 2007. Interventional Management of Stroke (IMS) II found a 9.9% rate of symptomatic intracerebral hemorrhage after combination IV-intra-arterial (IA) tissue-type plasminogen activator therapy was administered within 3 hours of acute stroke onset.
Further results from the MERCI and Multi-MERCI investigators have shown that successful recanalization of acute distal ICA and proximal middle cerebral artery occlusions can be achieved in 53% to 63% of patients using the MERCI retriever (Concentric Medical) alone or in combination with IV/IA thrombolytics, yet symptomatic hemorrhages occurred in 6% of those patients who were recanalized.
Another approach in those who fail MERCI retrieval has been to use angioplasty or self-expanding stents to compress friable clots and allow better penetration of thrombolytic agents. Recanalization rates of up to 89% with balloons and 79% with stents have been achieved in small numbers of patients.
Reports of aggressive revascularization of acute ICA and tandem ICA/middle cerebral artery occlusions using stents and intracranial thrombolysis have demonstrated the feasibility of this approach, again in small numbers of patients.
Attempts to identify prognostic factors for hemorrhagic complications and eventual clinical outcomes in patients undergoing these aggressive multimodal interventions showed that residual distal occlusions, tandem occlusions, larger initial pretreatment CT infarct size by Alberta Stroke Program Early CT Score (ASPECTS) score, hyperglycemia and use of both IA and IV thrombolytics were all associated with negative results. Novel mechanical revascularization strategies used deflated microballoon catheters and the Alligator retrieval device (Chestnut Medical Technologies) to open vessels that may be refractory to IA thrombolytics or the MERCI device.
There are new stents being used to assist in the coiling of wide-necked aneurysms, such as the closed-cell design Enterprise (Cordis Neurovascular, Inc), the electrodetachable, fully retrievable Solo (eV3 Neurovascular) and the covered, balloon-expandable Willis (Microport). Development of significant focal stenosis remains a problem, seen in up to 5.8% of stent-assisted cases. A novel approach is to use a high-coverage, endoluminal mesh to divert flow and thus induce aneurysm thrombosis. The Pipeline Neuroendovascular Device (Chestnut Medical Technologies) is a tubular, bimetallic implant with approximately 30% coverage by area. Preliminary experience in humans has been encouraging.
It is hoped that immunohistochemical and molecular biological data can be used to develop biologically active endovascular devices in the future. A novel method for depositing viable, migration capable fibroblasts on coils and successfully passing them through microcatheters may be a promising technique for endovascular intervention.
Intra-arterial (IA) therapies for acute stroke have evolved over the past decade. Despite the promising results of the PROACT II study, which demonstrated a 66% recanalization rate, substantially higher recanalization rates with IA pharmacologic thrombolysis have not been achieved over the past 7 years. The Food and Drug Administration recently approved a clot retrieval device (Merci retriever X5, X6; Concentric Medical, Mountain View, Calif.). Unfortunately, when used alone, the clot retriever is successful in only approximately 50% of cases, and multiple passes with this device are often required to achieve successful recanalization. IA thrombolytics administered concomitantly enhance the procedural success of this device but may increase the risk of hemorrhagic transformation of the reperfused infarction. There have been several reports of coronary stent implantation used for mechanical thrombolysis of recalcitrant occlusions. In a recent report, stent placement with balloon-mounted or self-expanding coronary stents was shown to be an independent predictor for recanalization of both intracranial and extracranial cerebrovascular occlusions. In another recent report, recanalization rates of 79% were achieved using balloon-mounted stent technology.
Self-expanding stents designed specifically for the cerebrovasculature can be delivered to target areas of intracranial stenosis with a success rate of >95% and an increased safety profile of deliverability because these stents are deployed at significantly lower pressures than balloon-mounted coronary stents. There has been an anecdotal report of the use of a self-expanding stent in the setting of acute symptomatic intracranial occlusion. In addition, a recent comparison of self-expanding and balloon-mounted stents in an animal model of acute embolic occlusion has shown no difference in the 2 stent groups with respect to recanalization rates.
This retrospective multicenter series demonstrates that the use of self-expanding stents is feasible in the setting of symptomatic medium- and large-vessel intracranial occlusions. With stent placement as a first-line mechanical treatment or as a “last-resort” maneuver, TIMI/TICI 2 or 3 revascularization was successfully obtained in 79% of the lesions in which stents were placed. This retrospective review suggests that focal occlusions limited to a single medium or large vessel, particularly solitary occlusions of the MCA or VBS, may be preferentially amenable to stent placement and thus can help clinicians to achieve improved rates of recanalization. In addition, gender may playa role in the success of self-expanding stent implantation: TIMI/TICI 2 or 3 flow was documented in all female patients studied, and female patients were more likely to achieve improved clinical outcomes as measured by NIHSS and mRS scores. Most importantly, our preliminary experience may lead to future pivotal studies that might aid clinicians to better stratify patients most likely to derive maximal clinical benefit from stent placement.
The use of other mechanical means has been reported to be effective in recanalization of acute occlusions. In the MERCI trial, overall recanalization rates (TIMI/TICI 2 or 3 flow) of 48% were achieved with the Merci mechanical clot retriever.
Several authors have proposed endovascular treatment with stent deployment for ICA dissection with high-grade stenosis or occlusion when anticoagulation fails to prevent a new ischemic event. In these cases, the MCA was patent.
We found that stent-assisted endovascular thrombolysis/thrombectomy compared favorably with IV rtPA thrombolysis.
This higher rate of MCA recanalization could be explained by carotid flow restoration, allowing direct access to the MCA thrombus.
Endovascular treatment could potentially extend the therapeutic window beyond 3 hours. Actually, in all cases in the endovascular group, MCA recanalization was obtained by 291 minutes.
Despite these promising preliminary results, potential drawbacks related to the procedure must be considered. Acute complications such as transient ischemic attack, ischemic stroke, femoral or carotid dissection, and death have been reported. Other potential hazards of endovascular treatment of carotid dissection could be observed, as they were in stenting of other cases of arteriopathy. In our series, 1 embolic stroke and 1 acute in-stent thrombosis occurred in the same patient. Despite this new infarction, we observed significant neurologic improvement in this patient, probably because the MCA remained patent. Late stent thrombosis has also been reported.